https://www.acwing.com/problem/content/description/792/
#include<stdio.h>
#include<math.h>
int main()
{
double n;
scanf("%lf",&n);
double l = -10000;
double r = 10000;
while(r-l > 1e-8)
{
double mid = (l+r) / 2;
if( mid*mid*mid >= n)
{
r = mid;
}
else
{
l = mid;
}
}
printf("%lf\n",l);
}